<!DOCTYPE html>
<html lang="en">
<head>
    <meta charset="UTF-8">
    <meta http-equiv="X-UA-Compatible" content="IE=edge">
    <meta name="viewport" content="width=device-width, initial-scale=1.0">
    <title>Document</title>
</head>
<style>
    *{
        margin:auto;
    }
    .header{
        /* margin:0 auto; */
        max-width:960px;
        height:100px;
        background:blue;
    }
    .content{
        margin: 0 auto;
        max-width:960px;
        height:400px;
        background:pink;
    }
    .footer{
        margin: 0 auto;
        max-width:960px;
        height:100px;
        background:burlywood;
    }
</style>
<body>
    <div class="header">header</div>
    <div class="content">content</div>
    <div class="footer">footer</div>
</body>
</html>